This harrier inhabits open swamps in northern Africa and Eurasia, between 30°N and 62°N. The birds of the south and south-west are largely sedentary, but those from the north and the north-east are mainly wintering in sub-Saharan Africa. About 10000 breeding pairs inhabit the European Union. Some populations have definitely increased in western Europe, but those of the southern part of the continent are steadily decreasing, e.g. in the Iberian Peninsula

This species is a bird of swamps, marshes, flood plains or rice fields and reed beds. On migration it is much less likely to be seen in dry open grassland than other harriers and principally follows river valleys or coasts, though it must cross dry areas sometimes. ln its winter quarters it is often very common, e.g. in rice fields in South India.

During courtship the male carries out spectacular aerobatics over the nest and surrounding area. He soars in high circles, sometimes flying with exaggerated wing beats, and occasionally calling. Sometimes the pair display together, when he dives down at her and she rolls over to present her talons. The nest is well hidden in the dense reed bed or other thick vegetation in shallow water. The female takes about 10 days to build the pile of sticks, reeds and grass that serves as a nest. Meanwhile, the male makes a platform for resting and feeding. Both parents add material to the main nest during fledging. The female incubates for 31-38 days per egg, usually starting with the first. The male provides for the female near the nest. For the first week or so the chicks are brooded by the female, who feeds them beak-to-beak, but later they feed themselves in the nest, often with some ferocity, especially if the female is not very attentive. During lean times the bigger chicks may kill and eat their smaller siblings. The male brings food in the typical harrier way, dropping it for the female to catch in the air. As the young develop, the female helps with the hunting. She can rear the brood on her own if her mate is killed or deserts her. After a month or so the chicks scatter into the surrounding vegetation. They fledge at 35-40 days. The male soon leaves after that, but they usually remain with the female for a further 15-25 days.

Being a good bit bigger than the Hen Harrier, the Marsh Harrier can take a wider variety of prey. During the breeding season his hunting area is reduced and it must take advantage of local abundances. At that time he concentrates on marsh birds and small mammals which are easily caught, relying on surprise rather than speed. The Harrier generally quarters flat areas at a height of only a few meters, always taking advantage of cover, sometimes hovering or performing impressive aerobatics before dropping with claws outstretched. Prey is sometimes spotted from a low perch. Birds taken include poultry, ducks, waders, coot, moorhen, water rail, gulls, young pheasants and partridges, and songbirds and their young. Mammals include voles, mice, rabbits, moles, rats and young hares. Frogs are also important.

This species has an estimated global Extent of Occurrence of 1,000,000-10,000,000 km2. It has a large global population estimated to be 100,000-1,000,000 individuals (Ferguson-Lees et al. 2001). Global population trends have not been quantified, but populations appear to be stable (Ferguson-Lees et al. 2001) so the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.

Mainly migratory in Northern & Eastern Europe and Central Asia; sedentary and dispersive in South of breeding range. Northern breeders winter from France and North Africa through Mediterranean to Turkey, Middle East and Nile Valley, and South to sub-Saharan Africa. Easternmost Asian populations winter in Indian Subcontinent and Sri Lanka.
Migration in Western Europe begins with young birds of the year in mid-August, followed by adults in September and October. Males migrate later than females and young, and arrive in wintering grounds later. The rate and extent of migration varies according to the place of origin, northern birds leaving earlier, moving faster and travelling further than do birds from Southern Europe, which may remain most of the winter quite close to their breeding areas. The southern migration from Europe follows well-marked routes through Gibraltar or the Bosphorus, and rarely crosses large bodies of water; they may reach high altitudes up to 9,000 feet when crossing mountain passes on migration, but usually favour low ground.
Northward migration begins again in February and March, and both at this time and in autumn they are more gregarious than usual, roosting communally in swamps like some other harriers, with up to 300 together in some races. The northward migration frequently crosses the Mediterranean, so that evidently they can cross large bodies of water if necessary. Returning birds arrive in their breeding haunts from late March onwards, as late as early May in the northern parts of the range. They generally migrate singly or in small parties, not in large flocks, but often roost gregariously even when hunting singly. In winter quarters the same individuals may frequent the same area for weeks at a time.

article number 1 Title
Main migratory direction of Marsh Harrier Circus aeruginosus: an analysis of recovery data of specimens ringed in Latvia from 1925 to 2004
Author(s): J?nis Reihmanis
Abstract: Th is paper describes the main migratory directions of the Latvian Marsh Harrier Circus aeruginosus population and provides an overview of recovery data. Th e study was based on analysis of recovery ..[more]..
Source: Acta Universitatis Latviensis, 2005, Vol. 691, Biology, pp. 51-57
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article number 2 Title
Nest-site selection by Marsh Harrier (Circus aeruginosus) in the shore belt of Helophytes on large lakes
Author(s): Vitas Stanevicius
Abstract: Nest-site selection by Marsh Harrier (Circus aeruginosus) was investigated on Lakes Meteliai and Obelija in 1983ñ1986 and Lake fialtytis in 1984ñ1986 in southern Lithuania. Fifty five breeding pairs..[more]..
Source: Acta Zoologica Lituanica, 2004, Volumen 14, Numerus 3
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article number 3 Title
Factors influencing nest material selection in Marsh Harrier (Circus aeruginosus)
Author(s): Vitas Stanevicius, Ausrys Balevicius
Abstract: Marsh Harrier used at least 30 plant species from natural and cultural landscapes and habitats for nest building on Lakes Meteliai, Obelija and fialtytis (southern Lithuania). Helophytes dominated a..[more]..
Source: Acta Zoologica Lituanica, 2005, Volumen 15, Numerus 1
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article number 4 Title
The effect of predation by Marsh Harriers Circus aeruginosus on the survival of ducklings and game bird chicks.
Author(s): Underhill-Day J.C.
Abstract: The level of predation by a pair of Marsh Harriers Circus aeruginosus on ducklings and gamebird chicks was calculated from observations of hunting ranges, feeding rates and diet, and estimates of the ..[more]..
Source: ARDEA 77 (1): 47-56.
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article number 5 Title
New material supplies in the Marsh Harrier Circus aeruginosus sexual roles daily and seasonal activity patterns and rainfall influence
Author(s): Fernandez C.
Abstract: Nest maintenance is an important part of parental care for the Marsh Harrier Circus aeruginosus throughout the entire breeding period. Nest material supply trips are mainly carried out by the female a..[more]..
Source: ARDEA 80 (2): 281-284
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article number 6 Title
Reproduction of the Marsh Harrier Circus aeruginosus in recent land reclamations in The Netherlands.
Author(s): Dijkstra C. & Zijlstra M.
Abstract: We studied temporal variation in reproductive performance of Marsh Harriers Circus aeruginosus in two land reclamations in The Netherlands, i.e. South Flevoland and the Lauwersmeerpolder, embanked in ..[more]..
Source: ARDEA 85 (1): 37-50.
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article number 7 Title
Changes in the frequency of prospecting fly-overs by Marsh Harriers Circus aeruginosus in relation to short-term fluctuations in dabbling duck abundance
Author(s): Fritz H., Guillemain M. & Guerin S.
Abstract: Wintering waterfowl gathering in large flocks during the day may be attractive to avian predators in a way similar to that of bird colonies. The response of Marsh Harriers to changes in dabbling duck ..[more]..
Source: ARDEA 88 (1): 9-16.
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article number 8 Title
Predation by a Marsh Harrier Circus aeruginosus on Yellow-legged Gull Larus michahellis nests
Author(s): Albert Bertolero
Abstract: This note reports a case of predation by an adult female Marsh Harrier Circus aeruginosus on three nests of Yellow-legged Gulls Larus michahellis at the Ebro Delta. The predation was observed on 4 A..[more]..
Source: Revista Catalana d'Ornitologia 19:38-40, 2002
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